JPH0711479A - Zinc alloy plated steel sheet and its production - Google Patents

Abstract

PURPOSE:To obtain excellent plating adhesion even under the severe conditions where a zinc alloy electroplated steel sheet, to which three-coat coating for automobile is applied, is liable to cause the peeling off of a plating layer due to pebbles and rock salt in a cold district. CONSTITUTION:The surface of a steel sheet 1 is coated with a nickel alloy at (1 to 1000)mg/m<2> nickel coating weight. The nickel alloy coated steel sheet is heated, by which a part or the whole of the nickel alloy is allowed to diffuse and penetrate into the steel sheet and a nickel diffused region 2 where nickel coating weight is regulated to (1 to 1000)mg/m<2> is formed. A zinc alloy plating layer 3 is formed on the above. This steel sheet has superior low temp. chipping resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc-based alloy-plated steel sheet which is excellent in low temperature chipping resistance (plating adhesion at low temperature) and suitable for steel sheets for automobiles, and a method for producing the same.

[0002]

2. Description of the Related Art In cold regions, rock salt is sprayed to prevent freezing of roads in winter. Corrosion of automobile bodies by the sprayed rock salt is a serious problem. Therefore, various anticorrosion steel sheets for automobiles have been developed and put into practical use, and the amount of use thereof is increasing.

In the corrosion of the car body, the outer surface rust of the car body is hit by pebbles and sprayed rock salt splashed from the road surface during traveling on the road surface, peeling off the paint on the car body surface, and scratches reaching the outer steel plate, Generated by water and sprayed salt invading.

In order to prevent such corrosion of the outer surface of the vehicle body,
For example, galvanized steel sheets are used. Due to its strong sacrificial anticorrosive action, the galvanized steel sheet sufficiently protects the steel sheet even if a flaw reaching the steel sheet is entered. However, when a steel sheet is coated, it has a drawback that the coating film swells from a flaw and rust easily occurs there.

Therefore, in recent years, Zn--Ni, Zn--Fe,
A zinc-based alloy plated steel sheet in which a zinc-based alloy plating such as Zn-Cr is formed into a single layer or a multi-layer has been developed, and these plated steel sheets show good corrosion resistance. However, these zinc-based alloy plating films have a drawback that the internal stress of the plating film is higher than that of the zinc plating film, and the plating adhesion to the steel sheet is weak.

Further, in cold regions in winter, the temperature drops to about -40 ° C., the shrinkage of the coating film progresses, and the plating adhesion becomes further lower, resulting in the peeling of the plating layer due to the above-mentioned pebbles and rock salt. It will be easier.

As a measure for improving the plating adhesion of a zinc-based alloy plated steel sheet, for example, JP-A-59-200789 is available.
And Japanese Patent Publication No. 3-44156. In these publications,
Cr, Mn, Fe, Co, Ni, Cu, Yn, Zn, C
Disclosed is a method in which a metal, such as d, Sb, or Pb, is used alone or as an alloy and is interposed between the zinc-based alloy plating and the base steel sheet. FIG. 1 (b) is a schematic sectional view of a zinc-based alloy plated steel sheet obtained by this method, 10 is a steel sheet, 11 is an intermediate layer such as Ni, and 12 is a zinc-based alloy plated layer.

Further, Japanese Patent Application Laid-Open No. 1-272791 discloses a measure for forming a Ni diffusion layer on the surface of a steel sheet by heating to enhance the plating adhesion of a zinc-based alloy plated steel sheet. Since heat treatment is performed after quality rolling,
At this point, the steel sheet hardens and loses its aging property.
It has a drawback that it cannot be applied to steel plates (BH steel plates) that require aging.

[0009]

The inventors of the present invention studied the low temperature pitting resistance of the zinc-based alloy plated steel sheet obtained by the above-mentioned manufacturing method and found that sufficient low temperature pitting resistance could not be obtained. found.

In the zinc-based alloy-plated steel sheet produced by the above-mentioned method, the electrodeposition strain (internal) between the zinc-based alloy-plated metal layer and the nickel-based alloy-plated metal layer (hereinafter referred to as an intermediate plating layer) interposed between the base steel sheet. (Stress) remains, and a boundary due to a difference in strain is clearly present between the steel sheet and the base steel sheet, so that delamination occurred at this boundary surface.

It is conceivable to reduce the thickness of the intermediate plating layer in order to reduce the electrodeposition strain of the intermediate plating layer and eliminate the boundaries of strain. However, if this is done, the thickness becomes too thin, which is the main cause. The low-temperature pitting resistance (plating adhesion), which is the object of improvement, could not be obtained. Therefore, under severe conditions such as 3-coat coating in cold regions (about -40 ° C), collision of high-speed pebbles, rock salt, etc., the low-temperature pitting resistance of zinc-based alloy plating is still insufficient even if the above method is used. It turned out to be.

Furthermore, since the intermediate layer has a discontinuity in the plating layer, a large potential gap is generated between the steel sheet and the plating layer, and as a result, corrosion resistance is likely to decrease. In view of the above circumstances, the inventors of the present invention have conducted repeated studies for the purpose of obtaining a zinc-based alloy electroplated steel sheet coated with a three-coat coating for automobiles even under the severe conditions as described above. It was

It has been conventionally known that nickel alloys show good results in an impact test (low temperature brittle fracture) at low temperature. The present inventor applies this nickel-based alloy to an intermediate plating layer, and further diffuses and permeates it into the steel to unclear the boundary between the two, and the stress difference between the zinc-based alloy plating and the steel sheet to be subsequently applied. It has been found that by making it possible to gradually reduce the thickness, good plating adhesion can be obtained even under the severe conditions as described above. It was also found that the diffusion resistance can minimize the potential gap, and thus the corrosion resistance can be improved.

The present invention has been made on the basis of the above findings, and an object thereof is to provide a plated steel sheet and a galvanized steel sheet which can obtain sufficient low-temperature chipping resistance of zinc-based alloy plating even under the severe conditions as described above. It is to provide the manufacturing method.

[0015]

In order to achieve this object, the manufacturing method of the present invention is such that a nickel-based alloy on the surface of a steel sheet has a Ni deposition amount of 1 to 1000 mg / m ² .
By electroplating and heating (annealing) this steel sheet preferably in a non-oxidizing atmosphere, part or all of the plated metal is permeated and diffused into the steel sheet. After that, the zinc-based alloy electroplated steel sheet having excellent low-temperature pitting resistance (plating adhesion) is characterized in that a predetermined amount of zinc-based alloy plating is subsequently applied. The plated steel sheet of the present invention is provided with a nickel diffusion region, a nickel layer, and a zinc alloy plating layer, if necessary, in this order on the steel sheet.

[0016]

The steel sheet is, for example, a hot rolled steel sheet or a cold thick sheet before annealing. The thickness of the steel plate is usually about 0.3 to 3.2 mm. To form a nickel diffusion region on the steel plate surface,
It is formed by depositing nickel or a nickel-based alloy on the surface of a steel sheet. The appropriate amount of nickel or nickel deposited on the surface of the steel sheet is 1 to 1000 mg / m ² . If the adhesion amount is less than the lower limit value, there is no remarkable effect of improving the low temperature pitting resistance. If the upper limit is exceeded, the effect of improving low temperature pitting resistance will be saturated.

The nickel content in the nickel-based alloy is appropriately selected depending on the amount of adhesion and the purpose, but is generally 2 to 100%, and as a component other than nickel, F is used.
One or more of e, Cr, Co, Mo, Mn, Cu, P, B, W and V can be applied. Specifically, N
Examples thereof include i-Fe alloy, Ni-Co alloy, and Ni-Cr alloy.

After applying nickel or a nickel-based alloy plating as a base plating, a heat treatment (annealing) is performed. The annealing temperature is 600 to 800 ° C in batch processing, and the annealing time is about 2
4 hours, 650-900 in continuous annealing line (CAL)
C. and soaking time of 50 to 200 seconds are preferable. The soaking time in CAL is 50 to 200 seconds, which is so short that a diffusion region cannot be usually formed sufficiently, but a sufficient diffusion region can be obtained by the method of the present invention for the following reasons. During annealing, steel is recrystallized, and at the same time, part or all of nickel or nickel-based alloy for undercoating permeates and diffuses into the steel, so that nickel diffusion is greater than nickel diffusion on recrystallized steel. Regions are extremely easily formed, and nickel diffusion regions can be obtained in the steel sheet continuously in the depth direction and uniformly in the width direction in a short time. The formation of the diffusion region reduces the electrodeposition strain in the nickel or nickel-based alloy plating layer, and the boundary surface between the two becomes unclear. The stress difference gradually and continuously decreases in this portion, and the low temperature pitting resistance is improved. The preferred diffusion region is the reduction of electrodeposition strain,
From the viewpoint of unclear boundary surface, the thickness is 0.01
It is preferable that the thickness is about 50 μm. When the heat treatment is performed on all of the nickel or nickel-based alloy plating layers, all of the nickel or nickel-based alloy plating layers become Ni diffusion regions. A part becomes the Ni diffusion region, and the nickel or nickel-based alloy plating layer remains on it.

After the diffusion treatment, zinc or a zinc alloy plating is applied on the nickel diffusion region and the nickel or nickel alloy plating layer. The amount of zinc-based alloy electroplating to be applied is not particularly limited, but a predetermined amount of plating, usually 5 to 60
g / m ² may be applied. A zinc-based alloy means Zn-
Ni, Zn-Fe, Zn-Co, Zn-Cr, Zn-N
i-Cr, Zn-Fe-Cr, Zn-Mn, Zn-Mn
-Zn-based alloys such as Cr, plating that combines these, or plating with a concentration gradient is included. The content of components other than zinc is not particularly limited, but in view of the blister resistance, it is desirable that the components other than zinc, alone or in combination, be contained in a total amount of 1 to 30 wt%. Specifically, Zn-Ni alloy, Zn
-Cr alloy, Zn-Co alloy, etc. are mentioned.

The production method of the present invention is applied to both sides or one side of the steel sheet as required. Further, the plated steel sheet of the present invention is not limited to the zinc-based alloy plated steel sheet having the above-mentioned configuration, but this steel sheet is further subjected to chromate treatment and / or an organic composite resin film to form a chromate film and / or an organic composite resin film. Including things. With this structure, the corrosion resistance is further improved. INDUSTRIAL APPLICABILITY The present invention can be applied to a steel sheet that requires aging because an Ni alloy layer is formed on the surface of the steel sheet during annealing and then temper rolling is performed.

[0021]

EXAMPLES Methods A to C are mentioned as specific methods for producing the zinc-based alloy plated steel sheet of the present invention. Method A: Hot-rolled steel sheet → Pickling (surface cleaning) → Nickel alloy plating (undercoating) (Note 1) → Cold rolling → Annealing → Temper rolling → Zinc alloy plating → Zinc alloy plated steel sheet (Product (Note 1) The amount of plating is determined according to the cold pressing rate so that the amount of plating after rolling is 1 to 1000 mg / m ² .

Method B: Hot-rolled steel sheet → pickling & nickel alloy plating → cold rolling → annealing → pressure adjustment → zinc alloy plating → zinc alloy plating steel sheet (product) In this case, pickling & nickel plating step (1) A method of putting a nickel-based plating solution in the pickling tank on the outlet side of the pickling line, arranging an electrode therein, and forming a nickel-based plating layer consistently in the pickling line, and (2) There is a method in which nickel ions or the like are added to the pickling line outlet side pickling tank to chemically form a nickel-based plating layer without electricity.

Examples of the method (2) include Ni-Co and Ni-Cu, which are metals more noble than Fe, and Ni-P and Ni-B, which are formed by adding hypophosphorous acid as a reducing agent. . According to this method B, the target plated steel sheet can be efficiently manufactured without increasing the number of steps.

Method C: Pickled hot rolled steel sheet → cold rolling → surface cleaning → nickel alloy plating (undercoating) → annealing → temper rolling → zinc alloy plating → zinc alloy plated steel sheet (product) Method According to C, nickel-based alloy plating (undercoating) is possible before and after cold rolling. Further, by using an unannealed plate as the steel plate, formation of a diffusion layer of a nickel-based alloy is promoted simultaneously with annealing. The reduction ratio of the temper rolling after annealing may be appropriately set depending on the steel type of the steel sheet.

Next, the manufacturing method based on the present invention (method A)
According to the above, various zinc-based alloy electroplated steel sheets were manufactured, and a low temperature pitting resistance test was performed after coating with three coats for automobiles. Further, the same low temperature pitting resistance test was carried out on a zinc-based alloy-plated steel sheet having a Ni content and a Zn content that fall outside the range of the present invention. The plating conditions and the low temperature chipping resistance of the plated steel sheet are shown in Tables 1 and 2. In addition, the same low temperature pitting resistance test was conducted also in the case where the Zn-based alloy layer was formed without diffusion of the Ni alloy layer of the present invention. Table 3 shows the plating conditions and the low temperature pitting resistance of the plated steel sheet. In Tables 1 to 3, the vertical column indicates the type of nickel alloy plating, the horizontal column indicates the type of zinc alloy plating, the left side of each numerical value indicates the adhesion amount mg / m ² of the nickel alloy plating, and the right column. Is the amount of zinc alloy plated g / m
² is shown. The plating solution used here has a pH of 0.5 to 0.5 for both the nickel-based alloy plating for the base and the zinc-based alloy plating.
It is a sulfate bath having a bath temperature of 2.5 to 50 to 90 ° C. The heat treatment (batch annealing) was performed at 750 ° C. for 24 hours.
Continuous annealing was performed at 720 ° C. for 60 seconds. Figure 1 (a)
Is a schematic cross-sectional view of the obtained zinc-based alloy-plated steel sheet.
Is a steel plate, 2 is a Ni diffusion region, and 3 is a Zn-based alloy layer.
The thickness (depth) of the obtained Ni diffusion region is 5 μm.

The low temperature chipping test is 0.7 × 70 ×
Immersion type phosphate treatment on a 150 mm test piece → cathin-on electrodeposition coating (20 μm) → intermediate coating (40 μm) → top coating (40
μm), the test piece was cooled to −40 ° C., and about 10 mg of pebbles were made to collide with the test piece at a speed of 170 km / H, and the result was an examination of plating peeling after taping.

The evaluation criteria are as follows. Evaluation ◯: Plating peeling is less than 1% Δ: Plating peeling is more than 2% and 5% or less ×: Plating peeling is more than 5% As is apparent from the results shown in Tables 1 to 3, those having an adhesion amount within the range of the present invention It can be seen that the low-temperature pitting resistance is remarkably good as compared with the case where the adhesion amount is out of the range of the present invention or the conventional case where the thermal diffusion treatment is not performed.

[0028]

As described above, according to the present invention, it is possible to improve the low temperature pitting resistance and prevent the deterioration of the corrosion resistance.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[Brief description of drawings]

FIG. 1A is a sectional view of a plated steel sheet obtained by the method of the present invention, and FIG. 1B is a sectional view of a plated steel sheet obtained by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steel plate, 2 ... Diffusion region of nickel and nickel-based alloy, 3 ... Zinc alloy layer

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C25D 3/56 DA B

Claims (3)

[Claims] 1. A steel plate, a nickel diffusion region in which nickel or a nickel-based alloy is diffused on the surface of the steel plate, and a zinc or zinc-based alloy plating layer formed on the nickel diffusion region, wherein nickel is attached to the nickel diffusion region. The amount is 1-100
Zinc-based alloy plated steel sheet with 0 mg / m ² . 2. A steel plate, a nickel diffusion region in which a nickel-based alloy is diffused on the steel plate surface, nickel or a nickel alloy layer formed on the nickel diffusion region, and zinc or zinc formed on the nickel or nickel alloy layer. And a nickel diffusion region and a nickel adhesion amount in the nickel or nickel alloy layer is 1 to 1000 m.
Zinc alloy plated steel sheet with g / m ² . 3. A step of depositing nickel or a nickel-based alloy on the surface of a steel sheet, and heating the steel sheet coated with nickel or a nickel-based alloy to recrystallize the steel sheet and at the same time part or all of the nickel-based alloy. A method for producing a zinc-based alloy-plated steel sheet excellent in low-temperature chipping resistance, comprising: a step of diffusing and permeating into a steel sheet; and a step of plating zinc or a zinc-based alloy on the surface of the diffused nickel or nickel-based alloy.